Please refer to FIG. 1 which is a schematic diagram showing a carriage module of a conventional image scanner. The carriage module includes an optical mechanism 11 accommodated in a housing 12 and a charge coupled device (CCD) 13 secured to the housing 12. As indicated by the arrows, the light reflected from an object to be scanned is focused by a lens device 112 via the guidance of the reflective mirrors 111, and then transferred to the CCD 13. In the carriage module structure of FIG. 1, the CCD 13 is secured onto a printed circuit board (PCB) 14, and further secured to the housing 12 of the carriage module by attaching the PCB 14 to the carriage housing 12 with screws 15. By moving the lens device 112, the object length, i.e. the distance between the scanned object and the lens 112, is adjusted. Since the CCD 13 is welded to the PCB 14, floating welding situation may occur, as shown in FIG. 2A. Consequently, the CCD face will not be perpendicular to the central line of the lens 112. Even if the CCD 13 is well welded to the PCB 14, the deflection situation of the CCD 13 relative to the carriage module 11 may also occur for a non-flat PCB, as shown in FIG. 2B. As such, the focusing results at different positions of the CCD 13 will vary. Thus, the scanning quality is deteriorated.
In order to solve this problem, another securing mechanism is developed, as shown in FIG. 3. In the carriage module as shown, an additional adjusting element 26 including plugs 27, which penetrate the carriage housing 22 via through holes, is provided to adjust the level of the CCD 23 as well as the distance between the lens 221 and the CCD 23. After the proper positions of the plugs are determined, the through holes are sealed to secure the CCD 23 to the carriage module housing 22. This mechanism, however, allows only a small degree of adjustment because of the small residue space of the plugs 27 in the through holes. Moreover, such adjustment is not easily accomplished and spends a lot of time.